1. Field of the Invention
The present invention relates to an optical fiber strain measuring apparatus which measures strain of an optical fiber by heterodyne detection of mixed light comprising reference light and backscattering light from the optical fiber.
2. Description of the Related Art
An optical fiber strain measuring apparatus is an apparatus which, in general, projects an optical pulse from one end of an optical fiber to be measured, takes out backscattering light produced in the optical fiber from the end into which the optical pulse was projected, subjects mixed light of the taken out backscattering light and continuous light having a certain wavelength (reference light) to heterodyne detection using a photodetector, and measures a distorted position in the optical fiber from a relation between a time since the optical fiber was projected and a detected signal.
As described above, since the optical strain measuring apparatus measures a distorted position based on the detection result of mixed light comprising the taken out backscattering light and the reference light, it is required that the strength and the like of the reference light is stable uniformly in order to perform a precise measurement.